Intrinsic Lifetime Research Articles

Electron transfer and intersystem crossing in the coumarin-anthracene electron donor-acceptor dyads

A series of compact coumarin (Cou)-anthracene (An) electron donor-acceptor dyads were prepared, in which the two units are directly connected at either 2- or 9- position of the An unit and the 3-position of the Cou unit to study the relationship between the molecular configuration, electronic coupling and the intersystem crossing (ISC) efficiency. Single crystal X-ray diffraction results indicate that the dihedral angles are 88.0° and 85.7°, respectively, in the dyads, in which the donor and acceptor are connected by 9- position of the An unit (Cou-9An and Cou-9AnCN). However, for Cou-2An the optimized ground state geometry indicates a more coplanar configuration with a dihedral angle of 38.6°. The solvent polarity-dependent singlet oxygen quantum yields (ΦΔ) of the orthogonal dyads (Cou-9An and Cou-9AnCN) are 39% (in acetonitrile) and 64% (in dichloromethane), respectively. whereas ΦΔ is negligible for the coplanar dyad (Cou-2An). These results indicated that orthogonal geometry is beneficial to spin−orbit charge transfer ISC (SOCT-ISC) mechanism. Nanosecond transient absorption spectra demonstrated that the lowest triplet state was mainly localized on An unit in Cou-9An and Cou-9AnCN, with the intrinsic triplet state lifetime of 234 and 207 μs, respectively. Triplet state delocalization was observed for Cou-2An, which prolongs the triplet state lifetime to 742 μs. Femtosecond transient absorption spectra results indicated fast charge separation (CS, 0.36−0.41 ps) and slow charge recombination (CR, 2.1−2.8 ns) in the orthogonal dyads. Time-resolved electron paramagnetic resonance (TREPR) spectra further confirmed the SOCT-ISC mechanism in the orthogonal dyads (Cou-9An and Cou-9AnCN), however, the SOCT-ISC and spin orbit ISC (SO-ISC) mechanism are both responsible for the triplet state formation in the coplanar dyad (Cou-2An). Electron spin polarization (ESP) pattern of the triplet state TREPR spectra of Cou-9An and Cou-9AnCN is (a,e,a,e,a,e), however, ESP phase pattern of (e,a,e,a,e,a) and (e,e,e,a,a,a) were observed for the two triplet states required for the simulation of the TREPR spectrum of Cou-2An, which indicated that ESP patterns of triplet state not only depend on the molecular geometry, but also on the structure of the electron donor and acceptor.

Role of La 5p in Bulk and Quantum-Confined Solids Probed by the La 5p54f1 3D1 Excitonic Final State of Resonant Inelastic X-ray Scattering

The varied electronic localization of rare earth elements is essential to functional materials and a key to tailoring their properties. We establish with unprecedented spectral resolution the excitonic nature of the lanthanum 5p54f1 3D1 and 3D2 final states of resonant inelastic X-ray scattering (RIXS) at the La N4,5 edges. We extract the intrinsic lifetime, energy distance, and relative intensity ratio from single crystal LaAlO3 and construct an empirical model. With help of the model, we precisely determine the RIXS 3D1 final state position and identify La 5p as a descriptor of covalency with the host material. For metallic lanthanum, La3+ ions in mixed-covalent-ionic simple oxides and phosphates, and ionic salts alike, we find a sizable chemical shift, indicating band-like and free-ion-like La. The different electronic relaxation of the La 5p5 hole and the La 4f1 electron is discussed with local and nonlocal screening contributions. In addition, the energetics of the excitonic La 5p54f1 Coulomb attraction is quantified in its variation from lanthanum metal to mixed-covalent-ionic La2O3 and the ionic LaF3 salt. The power of the approach and analysis is applied to map the influence of geometric quantum confinement to La 5p sharing within quantum dots and quantum wires in comparison to bulk-like microrods of monoclinic LaPO4.

How Infrared Singularities Affect Nambu–Goldstone Bosons at Finite Temperatures

Ordered phases realized through broken continuous symmetries embrace long-range order-parameter fluctuations as manifest in the power-law decays of both the transverse and longitudinal correlations, which are similar to those at the second-order transition point. We calculate the transverse one-loop correction to the dispersion relation of nonrelativistic Nambu-Goldstone (NG) bosons at finite temperatures, assuming that they have well-defined dispersion relations with some integer exponents. It is found that the transverse correlations make the lifetime of the NG bosons vanish right on the assumed dispersion curve below three dimensions at finite temperatures. Combined with the vanishing of the longitudinal "mass", the result indicates that the correlations generally bring both an intrinsic lifetime to the excitations and a qualitative change in the dispersion relation at long wavelengths below three dimensions at finite temperatures, unless it is protected by some conservation law. A more detailed calculation performed specifically on a single-component Bose-Einstein condensate reveals that the gapless Bogoliubov mode predicted by the perturbative treatment is modified substantially after incorporating the correlations to have (i) an intrinsic lifetime and (ii) a peak shift at long wavelengths from the linear dispersion relation. Thus, the NG bosons may be fluctuating intrinsically into and out of the ordered "vacuum" to maintain the order temporally.

White Light-Emitting Electrochemical Cells Employing Phosphor-Sensitized Thermally Activated Delayed Fluorescence to Approach All-Phosphorescent Device Efficiencies.

Solid-state light-emitting electrochemical cells (LECs) show promising advantages of simple device architecture, low operation voltage, and insensitivity to the electrode work functions such that they have high potential in low-cost display and lighting applications. In this work, novel white LECs based on phosphor-sensitized thermally activated delayed fluorescence (TADF) are proposed. The emissive layer of these white LECs is composed of a blue-green phosphorescent host doped with a deep-red TADF guest. Efficient singlet-to-triplet intersystem crossing (ISC) on the phosphorescent host and the subsequent Förster energy transfer from the host triplet excitons to guest singlet excitons can make use of both singlet and triplet excitons on the host. With the good spectral overlap between the host emission and the guest absorption, 0.075 wt.% guest doping is sufficient to cause substantial energy transfer efficiency (ca. 40 %). In addition, such a low guest concentration also reduces the self-quenching effect and a high photoluminescence quantum yield of up to 84 % ensures high device efficiency. The phosphor-sensitized TADF white LECs indeed show a high external quantum efficiency of 9.6 %, which is comparable with all-phosphorescent white LECs. By employing diffusive substrates to extract the light trapped in the substrate, the device efficiency can be further improved by ca. 50 %. In the meantime, the intrinsic EL spectrum and device lifetime of the white LECs recover since the microcavity effect is destroyed. This work successfully demonstrates that the phosphor-sensitized TADF white LECs are potential candidates for efficient white light-emitting devices.

Electron Lifetime of Over One Month in Disordered Organic Solid-State Films.

Understanding intrinsic carrier lifetime in disordered organic solid-state semiconductors is essential for improving device performance in not only molecule-based optoelectronic devices such as organic solar cells (OSC) but also photocatalysts used for producing solar fuel cells. Carriers in disordered films are generally thought to have short lifetimes on a scale ranging from nanoseconds to milliseconds. These short carrier lifetimes cause loss of charges in OSCs and low quantum yields in photocatalysts and impede the future application of organic semiconductors to, for example, charge-storage-based memory devices. This study reports an ultralong intrinsic carrier lifetime of more than one month in a disordered film of an organic semiconductor stored at room temperature without external power. This extraordinary lifetime, which is several orders of magnitude longer than that generally believed possible in conventional organic semiconductors, arises from carrier stabilization by spontaneous orientation polarization, excited spin-triplet recycling, and blocking of recombination processes in disordered films.

Estimation of prolonged lifetimes of excited states of neutral oxygen atom (OI) by time-resolved laser-induced breakdown spectroscopy (TR-LIBS)

Lifetimes of the upper states of excited oxygen atoms corresponding to transitions to the common lower state in the case of the emission lines around 777 nm and 844 nm have been estimated by measuring the line intensities as a function of the delay time between the Q-switching of the laser and the opening of the window of the ICCD. In the case of the emission line around 777 nm, resulting from the transitions from the three very closely spaced upper energy levels, 2s2 2p3 (4S0) 3p5P3 (777.194 nm), 2s2 2p3 (4S0) 3p5P2 (777.417 nm) and 2s2 2p3 (4S0) 3p5P1 (777.539 nm) to the common lower energy level 2s2 2p3 (4S0) 3s5S2, the lifetime was measured to be 253 ns. Similarly, in the case of the emission-line around 844 nm, resulting from the transitions from the three very closely spaced upper energy levels 2s2 2p3 (4S0) 3p3P0 (844.625 nm), 2s2 2p3 (4S0) 3p3P2 (844.636 nm) and 2s2 2p3 (4S0) 3p3P1 (844.676 nm) to the common lower energy level 2p3 (4S0) 3s3S1, the lifetime was measured to be 278 ns by this technique. The measured lifetimes in our experiment, for both 777 nm and 844 nm atomic transition lines of oxygen (O), are almost nine times higher than the theoretical value. Self-absorption and radiation trapping are possible mechanisms responsible for the mismatch between measured and intrinsic lifetimes. Last but not least, utilizing the TR-LIBS technique is yet another incredible application to estimate the prolonged lifetime of closely spaced excited states of an atom in the presence of self-absorption and radiation trapping. The average plasma cooling temperature (excitation temperature) lifetime was found to be 1183 ns, which is compatible with the previously reported values. J. Bangladesh Acad. Sci. 46(2); 175-183: December 2022

Dark Singlet Exciton Sensitized Triplet Energy Transfer Across the CsPbBr3 Nanoplate‐Organic Interface

AbstractSemiconductor nanocrystals (NCs) sensitized triplet energy transfer (TET) provides a promising alternative for achieving efficient triplet‐triplet annihilation up‐conversion (TTA‐UC). However, the study on the role of NC's exciton fine structure in TET, which is important to further enhance the TET efficiency, is still limited. Herein, the respective contribution of bright/dark exciton to TET using 1‐naphthoic acid (mediator) decorated 2 nm thick CsPbBr3 nanoplates as the model system is studied. The well‐characterized and unique exciton fine structure and large bright‐dark splitting energy of CsPbBr3 nanoplates provide an ideal platform to unambiguously explore the TET between dark singlet exciton and mediator. By using time‐resolved temperature dependent optical spectroscopy, the direct participation of dark singlet state in the TET process is proved and also point out that the dark singlet exciton to mediator TET is the major energy transfer pathway, which is due to the ill‐defined nature of exciton's spin in strongly confined nanoplates and dark exciton's long intrinsic lifetime. Finally, in combination with 2,5‐diphenyloxazole as annihilator, mediator decorated CsPbBr3 nanoplates can convert visible to ultraviolet light with a maximum photon gain of 0.75 eV under a low threshold of ≈0.76 W cm−2.

Er3+ doped Ba2GdV3O11: Synthesis and characterization for crystal and photoluminescent features of bright green emitting nanophosphor

The synthesis of a green glowing series of Ba2Gd(1-x)ErxV3O11 (x = 0.01–0.05) has been accomplished through a simple route of solution combustion aided with urea. The X-ray fed diffraction leads to particular patterns for samples of a distinct phase prototype and hence, helps in establishing a similarity among erbium doped structures with that of the parent host. The electron microscopy of transmitting (TEM) and scanning (SEM) nature distinguish the dimension and surface related features of the synthesized nanophosphor, respectively. The even possession of different initial elements by the sample, is supported by energy dispersive spectroscopy (EDS) oriented mapping technique. The band gap for Ba2Gd0.98Er0.02V3O11 has been estimated to be 3.60 eV. The 1A1 → 1T1,2 transition lead by 345 nm of wavelength causes green luminescence in Er3+ doped Ba2GdV3O11 nanophosphors due to 3T2,1 → 1A1 (494 nm), 2H11/2 → 4I15/2 (527 nm) and 4S3/2 → 4I15/2 (556 nm) transition. The quenching of luminescence post 2 mol% concentration of Er3+ is accredited to dipole-dipole contact as per Dexter's theory. The intrinsic lifetime (8.823 ms), average lifetime (4.479 ms), non-radiative rates (109.891 s−1) along with quantum efficiency (51%), CIE x (= 0.1953), y (= 0.3320) coordinates present Ba2Gd0.98Er0.02V3O11 as a capable green emitting nanophosphor for RGB phosphors in lighting technology.

Accelerated performance optimization of drive axle housings based on the pseudo-damage reservation method

The pseudo-damage reservation method (PDRM) is proposed and applied for improving the efficiency of mature drive axle housing (DAH) optimization for the first time. Additionally, the PDRM can substantially reduce the period of the fatigue bench testing. Thereafter, the fatigue life of DAH products is calculated using the inertia relief method with the initial load spectrum and the accelerated load spectrum. Simultaneously, the PDRM’s life error is 1.6%, which meets the engineering accuracy requirements. Ultimately, with the first-order intrinsic frequency and lifetime as the constraints and the weights as the optimization objectives, five design variables are selected to obtain the optimized solutions by the NSGA-II. The optimization results show that the optimized DAH reduces the weight by 13.9%, the material cost by 11.7%, the fatigue test period by 34.9%, and the computational effort by 26.5%. Thus, the optimization solution through the PDRM is efficient, economical, and reliable, which provides a good reference for the low-cost, sustainable production of DAHs.

Polarized spectroscopic properties and 1046 nm laser operation of Yb3+:Ca3TaGa3Si2O14 crystal

A Yb3+:Ca3TaGa3Si2O14 single crystal was grown by the Czochralski method. Polarized absorption and fluorescence spectra of the crystal were measured at room temperature. The peak absorption cross sections at 977 nm are 3.69 × 10−20 and 2.03 × 10−20 cm2 for σ and π polarizations, respectively. The crystal has a broad gain band with a full width at half-maximum of 58 nm around 1 μm for σ polarization when the inversion parameter is 0.2. The intrinsic fluorescence lifetime of the 2F5/2 multiplet of the crystal was fitted to be 634 μs. Pumped by a 976 nm diode laser, a 1046 nm continuous-wave laser with a maximum output power of 2.8 W and a slope efficiency of 52.6% was achieved in the crystal. The results show the Yb3+:Ca3TaGa3Si2O14 crystal may be a potential gain medium for tunable and ultrashort pulse lasers at 1 μm.

Accelerated aging of all-inorganic, interface-stabilized perovskite solar cells.

To understand degradation routes and improve the stability of perovskite solar cells (PSCs), accelerated aging tests are needed. Here, we use elevated temperatures (up to 110°C) to quantify the accelerated degradation of encapsulated CsPbI3 PSCs under constant illumination. Incorporating a two-dimensional (2D) Cs2PbI2Cl2 capping layer between the perovskite active layer and hole-transport layer stabilizes the interface while increasing power conversion efficiency of the all-inorganic PSCs from 14.9 to 17.4%. Devices with this 2D capping layer did not degrade at 35°C and required >2100 hours at 110°C under constant illumination to degrade by 20% of their initial efficiency. Degradation acceleration factors based on the observed Arrhenius temperature dependence predict intrinsic lifetimes of 51,000 ± 7000 hours (>5 years) operating continuously at 35°C.

Coherent and Incoherent Tunneling into Yu-Shiba-Rusinov States Revealed by Atomic Scale Shot-Noise Spectroscopy.

The pair breaking potential of individual magnetic impurities in s-wave superconductors generates localized states inside the superconducting gap commonly referred to as Yu-Shiba-Rusinov (YSR) states whose isolated nature makes them promising building blocks for artificial structures that may host Majorana fermions. One of the challenges in this endeavor is to understand their intrinsic lifetime, ℏ/Λ, which is expected to be limited by the inelastic coupling with the continuum thus leading to decoherence. Here we use shot-noise scanning tunneling microscopy to reveal that electron tunneling into superconducting 2H-NbSe_{2} mediated by YSR states is not Poissonian, but ordered as a function of time, as evidenced by a reduction of the noise. Moreover, our data show the concomitant transfer of charges e and 2e, indicating that incoherent single particle and coherent Andreev processes operate simultaneously. From the quantitative agreement between experiment and theory we obtain Λ=1 μeV≪k_{B}T demonstrating that shot noise can probe energy scales and timescales inaccessible by conventional spectroscopy whose resolution is thermally limited.

Abstract 2472: Tumor/normal and live/dead classification in live tumor fragments using label-free multiphoton microscopy

Abstract We have developed a live tumor fragment (LTF) platform for predicting clinical response to cancer drugs. The success of this approach depends on screening tissue fragments derived from biopsies and excisions before drug treatment to select those that have acceptable levels of viability and tumor content. To enable this screening, we are developing label-free methods for integrated assessment of LTF histology, viability, and metabolic status using intrinsic multiphoton-excited fluorescence lifetime microscopy (MP-FLIM). We cut live EMT6 tumors and mammary fat pad into rectangular fragments that were then sorted and cultured in glass-bottomed multi-well plates. To induce cancer cell death, we treated one group with a therapeutic agent, e.g., the multi-kinase inhibitor, staurosporine, or the alkylating agent, cisplatin. Before and after treatment, we imaged LTF structure and metabolic status based on the intrinsically fluorescent metabolic co-factors nicotinamide dinucleotides (NAD(P)H) and flavin adenine dinucleotides (FAD) fluorescence intensity and lifetime using dual-excitation multiphoton microscopy. As a ground truth viability reference, we then stained and re-imaged the fragments using nuclear and cell viability probes such as Hoechst, SYTOX, TMRE and/or propidium iodide (PI). We analyzed the data by fitting fluorescence decay curves with dual or triple exponents to generate images of lifetime parameters, including the mean and individual component lifetimes and amplitudes. Finally, we co-registered the extrinsically labeled and autofluorescent lifetime images for 3D spatial analysis using commercial and custom software. We verified the methods using monolayer cell cultures and ATP luminescence and flow cytometry viability assays. Image spatial heterogeneity was quantified utilizing entropy metrics. Intrinsic contrast from multiphoton imaging revealed cellular and tissue structures. The median entropy was higher and its distribution negatively skewed for EMT6 (p<0.01), allowing us to distinguish tumor from its corresponding normal tissue of origin. In viable cells, nuclei were distinguishable from the cytoplasm via higher cytoplasmic NADH signal. Upon loss of cell viability, nuclear NADH signals increased, with characteristically short lifetimes, and the overall NADH intensity decreased, reducing the contrast between nuclei and their surrounding cytoplasm. We detected an increase in the whole fragment mean lifetime (τm p<0.002) and concomitant decrease in the short lifetime component (α1 p< 0.002) within 24 hours of staurosporine exposure. We have demonstrated that MP-FLIM can distinguish tumor from normal and live from dead in LTFs without labels. This approach will facilitate selection of fragments with acceptable viability and tumor content for subsequent drug treatment as part of a platform built for personalizing cancer therapy. Citation Format: Jonathan Ouellette, John Rafter, Kelsey Tweed, Leung Kau Tang, Christina Scribano, Pichet Adstamongkonkul, Mikaela Schultz, Justine Coburn, Maged Aldeeb, Neil Anthony, Christin Johnson, Kevin Eliceiri, Jonathan Oliner, Tomasz Zal. Tumor/normal and live/dead classification in live tumor fragments using label-free multiphoton microscopy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2472.

Naphthalimide-Carbazole Compact Electron Donor-Acceptor Dyads: Effect of Molecular Geometry and Electron-Donating Capacity on the Spin-Orbit Charge Transfer Intersystem Crossing.

We prepared a series of naphthalimide (NI)-carbazole (Cz) compact electron donor-acceptor dyads showing different substitution positions, C-N/C-C linkers, and conformation restriction magnitudes to study the spin-orbit charge transfer intersystem crossing (SOCT-ISC). The varied conformation restrictions lead to different dihedral angles between the donor and acceptor (37°-81°) and electronic coupling magnitude (matrix elements V: 1290-3070 cm-1). Based on the comparison between the dyads containing C-N and C-C linkers, we found that a large dihedral angle between the donor and acceptor is favorable to efficient SOCT-ISC. For one dyad, the singlet oxygen quantum yield (ΦΔ) is up to 84.4% (in dichloromethane), which is much higher than that of the previously reported NI-phenothiazine (PTZ) analogue dyad (ΦΔ = 16.0% in n-hexane). The intrinsic triplet state lifetime (τT) is 270 μs, longer than that accessed by the heavy atom effect (75.2 μs). As compared with the NI-PTZ analogue dyad, the Cz unit in the current dyads is a weaker electron donor than PTZ. Thus, a higher CT state energy in NI-Cz dyads was observed, which makes the SOCT-ISC efficient in solvents with a wide range of polarities. Meanwhile, the localized triplet state (3LE) becomes the lowest-lying state in the NI-Cz dyads, which is different from the triplet charge transfer (3CT) state observed in the analogue NI-PTZ dyad. Moreover, the large energy gap between the CT and 3LE states inhibits the reverse ISC; as a result, no thermally activated delayed fluorescence was observed for the current NI-Cz dyads.

Charge Separation and Intersystem Crossing in Homo- and Hetero-Compact Naphthalimide Dimers.

Naphthalimide (NI) homo- and hetero-dimers adopting orthogonal geometry were prepared to study photo-induced symmetry-breaking charge transfer (SBCT) and charge recombination (CR)-induced intersystem crossing (ISC). The two moieties in the dimer are connected either at the 3-C or 4-C position of the NI unit. The photophysical properties of the dimers were studied with steady-state and transient absorption spectroscopic methods. Significant CT only occurs for the hetero-dimer, in which one NI unit has a 4-amino substituent and the other NI unit is without it. The CR-induced ISC is most efficient for this dimer (singlet oxygen quantum yield ΦΔ = 50.3%). For the homo-dimer, in which both NI units did not present amino substitution, SBCT was not observed. Based on the electrochemical studies, we propose that the absence of SBCT for the homo-dimer is attributed to its high oxidation potential and low reduction potential. Femtosecond transient absorption (fs TA) spectra show that there is no charge separation (CS) for the homo-dimer. Nanosecond transient absorption spectroscopy indicate the formation of a triplet state with electron delocalization for the homo dimer, with a lifetime of 72.0 μs, while for the hetero dimer a triplet state with an intrinsic lifetime of 206.4 μs is observed. CS (11.6 ps) and slow CR-induced ISC (>1.5 ns) were observed for the hetero-dimer. Time-resolved electron paramagnetic resonance spectra give the zero-field splitting parameters (|D| = 1894 MHz and |E| = 111 MHz) and electron spin polarization patterns (e, e, e, a, a, a) for the triplet state of the hetero-dimer, inferring that the triplet state of the hetero-dimer is confined on the amino-substituted NI moiety.

Fluorescence Lifetime Phasor Analysis of the Decamer-Dimer Equilibrium of Human Peroxiredoxin 1.

Protein self-assembly is a common feature in biology and is often required for a myriad of fundamental processes, such as enzyme activity, signal transduction, and transport of solutes across membranes, among others. There are several techniques to find and assess homo-oligomer formation in proteins. Naturally, all these methods have their limitations, meaning that at least two or more different approaches are needed to characterize a case study. Herein, we present a new method to study protein associations using intrinsic fluorescence lifetime with phasors. In this case, the method is applied to determine the equilibrium dissociation constant (KD) of human peroxiredoxin 1 (hPrx1), an efficient cysteine-dependent peroxidase, that has a quaternary structure comprised of five head-to-tail homodimers non-covalently arranged in a decamer. The hPrx1 oligomeric state not only affects its activity but also its association with other proteins. The excited state lifetime of hPrx1 has distinct values at high and low concentrations, suggesting the presence of two different species. Phasor analysis of hPrx1 emission lifetime allowed for the identification and quantification of hPrx1 decamers, dimers, and their mixture at diverse protein concentrations. Using phasor algebra, we calculated the fraction of hPrx1 decamers at different concentrations and obtained KD (1.1 × 10−24 M4) and C0.5 (1.36 μM) values for the decamer–dimer equilibrium. The results were validated and compared with size exclusion chromatography. In addition, spectral phasors provided similar results despite the small differences in emission spectra as a function of hPrx1 concentration. The phasor approach was shown to be a highly sensitive and quantitative method to assess protein oligomerization and an attractive addition to the biophysicist’s toolkit.

Optical absorption of interlayer excitons in transition-metal dichalcogenide heterostructures.

Interlayer excitons, electron-hole pairs bound across two monolayer van der Waals semiconductors, offer promising electrical tunability and localizability. Because such excitons display weak electron-hole overlap, most studies have examined only the lowest-energy excitons through photoluminescence. We directly measured the dielectric response of interlayer excitons, which we accessed using their static electric dipole moment. We thereby determined an intrinsic radiative lifetime of 0.40 nanoseconds for the lowest direct-gap interlayer exciton in a tungsten diselenide/molybdenum diselenide heterostructure. We found that differences in electric field and twist angle induced trends in exciton transition strengths and energies, which could be related to wave function overlap, moiré confinement, and atomic reconstruction. Through comparison with photoluminescence spectra, this study identifies a momentum-indirect emission mechanism. Characterization of the absorption is key for applications relying on light-matter interactions.

Label-Free Characterization of Amyloids and Alpha-Synuclein Polymorphs by Exploiting Their Intrinsic Fluorescence Property.

Conventional in vitro aggregation assays often involve tagging with extrinsic fluorophores, which can interfere with aggregation. We propose the use of intrinsic amyloid fluorescence lifetime probed using two-photon excitation and represented by model-free phasor plots as a label-free assay to characterize the amyloid structure. Intrinsic amyloid fluorescence arises from the structured packing of β-sheets in amyloids and is independent of aromatic-based fluorescence. We show that different amyloids [i.e., α-Synuclein (αS), β-Lactoglobulin (βLG), and TasA] and different polymorphic populations of αS (induced by aggregation in salt-free and salt buffers mimicking the intra-/extracellular environments) can be differentiated by their unique fluorescence lifetimes. Moreover, we observe that disaggregation of the preformed fibrils of αS and βLG leads to increased fluorescence lifetimes, distinct from those of their fibrillar counterparts. Our assay presents a medium-throughput method for rapid classification of amyloids and their polymorphs (the latter of which recent studies have shown lead to different disease pathologies) and for testing small-molecule inhibitory compounds.

High power downconversion deep-red emission from Ho3+-doped fiber lasers

Abstract It has been a big challenge in decades for Ho3+-doped fiber laser to produce high emission power in deep-red due to its intrinsic long carrier lifetime in 5I7 energy level. Here, we advance the development of this visible fiber lasers by a novel pumping method that leverages the advantages of blue laser diode downconversion mechanisms to fully pumping, while shortening the lifetime of the lower energy level of the deep-red laser through excited state absorption. For the first time, we demonstrate a downconversion fiber laser using a single wavelength of 532 nm solid-state laser pump source to excite the Ho3+-doped ZBLAN fiber, which achieves a record high maximum output power of 1.64 W at 752.10 nm, as well as free-running of deep-red lasers with watt-level output. This technology represents a milestone in high power deep-red fiber lasers. Importantly, it is readily to be extended to other wavelengths that evidenced its huge application potentials in fiber laser industry.

Optical transition properties, energy transfer upconversion luminescence, and temperature-sensing characteristics of Tm3+/Yb3+ Co-doped oxyfluoride tellurite glass

The optical transition properties of Tm3+ in oxyfluoride tellurite glass were determined by the Judd–Ofelt theory. The radiative transition rates, fluorescence branching ratios, and intrinsic lifetime for interesting transitions or level were obtained. The optimum doping concentration of Tm3+ for sample was examined, and the optimal concentration for upconversion luminescence was 0.1% Tm2O3. The main reason for concentration quenching was nonradiative energy transfer through the cross-relaxation mechanism. In addition, two-photon processes for near-infrared 3H4→3H6 emission and three-photon processes for blue 1G4→3H6 emission of Tm3+ were confirmed by analyzing the dependence of upconversion intensities on the 980 nm fiber laser. The temperature-sensing properties of Tm3+ in oxyfluoride tellurite glass were investigated using 3F2,3 → 3H6 (698 nm) and 3H4→3H6 (801 nm) excited at 980 nm, and the 3F2,3 and 3H4 states of Tm3+ were thermally coupled levels.